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	<meta charset="UTF-8">
	<title>css选择器</title>
	<style type="text/css">
	   /*p.special,#three,h1{font-size:50px;}
	   p{color:red;}
	   .special{color:blue;}	   
	   .one{text-decoration: underline;}
	   #two{color:green;}*/
	   /**{font-size:50px;
	     color:blue;}*/
	    /*em{color:red;}*/
	    .classred{color:red;}
	    p em{color:blue;}
        h1.special em{color:orange;}
        em{color:red;} 
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	<h1 class="special"><em>CSS</em>是什么</h1>
	<p><em>CSS</em>层叠样式</p>
	<p class="special one">用于定义HTML内容在浏览器中的显示样式</p>
	<p><em>CSS</em>样式由选择器和声明组成</p>
	<div>
		<h1 id="two"><em class="classred">css</em>使用方法</h1>
		<ul id="three">
			<li>行内样式</li>
			<li>内部样式</li>
			<li>外部样式</li>
			<li>导入式</li>	
		</ul>
		<h1><em>css</em>选择器</h1>
		<ul>
			<li>标签选择器</li>
			<li>ID选择器</li>
			<li>类选择器</li>
			<li>后代选择器</li>
		</ul>
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